Photocatalyst composite and process for producing the same

ABSTRACT

A photocatalyst composite is provided which comprise a substrate having particles of a photocatalyst such as titanium oxide, adhered thereon via a less degradative adhesive such as a fluorinated polymer comprising a copolymer of a vinyl ester and/or vinyl ether and a fluoroolefin, or a silicon based polymer or cement. Furthermore, a process for producing the photocatalyst composite and a coating composition containing the photocatalyst composite are provided.

This is a divisional of application Ser. No. 08/638,739, filed Apr. 29,1996, now abandoned; which is a continuation of application Ser. No.08/555,548 filed Nov. 9, 1995, now issued as U.S. Pat. No. 5,547,823;which is a continuation of application Ser. No. 08/266,464, filed Jun.27, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photocatalyst composite comprising asubstrate having photocatalyst particles adhered thereon and a processfor producing the same.

2. Description of Related Art

Exposure of photocatalyst particles to an irradiation of a wavelengthcorresponding to not less than the band gap energy causes thephotoexcitation of electrons into a conduction band with a correspondinggeneration of holes in a valence band. The strong reduction power of theelectrons and the strong oxidation power of the holes generated by thisoptical excitation have been utilized in decomposition and purificationof organic materials as well as in decomposition of water. Thephotocatalyst particles to be used in such treatments are usuallydeposited on a substrate of dimensions larger than the photocatalystparticles in order to prevent them from scattering into the air orexhausting out of the system and subsequently to provide for easyseparation of the photocatalyst from the treatment system. Thedeposition of photocatalyst particles on a substrate has beenaccomplished by a method comprising sintering the photocatalystparticles on the substrate at a temperature of 400° C. or higher toadhere the particles to the substrate, or a method comprising spraying aprecursor, which can be converted to photocatalyst through thermaldecomposition, onto a substrate heated at a temperature of about 400°C., thereby adhering the particles on the substrate. Alternatively,there has been proposed a method immobilizing photocatalyst particlesusing a certain type of fluorinated polymer. For example, JapanesePatent KOKAI (Laid-open) No. Hei 4-284851 discloses a method comprisinglaminating a mixture of photocatalyst particles and a fluorinatedpolymer and compressing the laminate under a pressure. Japanese PatentKOKAI (Laid-open) No. Hei 4-334552 discloses a method comprisingthermally fusing a fluorinated polymer to adhere photocatalyst particlesthereto.

Recently, an attempt has been made to use photocatalyst particles fordecomposition of deleterious materials, malodorous materials and oilysubstances in the waste products produced daily in inhabitantcircumstances as well as purification and sterilization of the wasteproducts. Thus the photocatalyst particles have found ever broadeningareas of application. In this regard, there is a need for a methodcapable of adhering firmly photocatalyst particles onto any substrate,which adhesion can be maintained over an extended period of time,without losing their photocatalytic function. Unfortunately, the priorart methods as described above suffer from insufficient adhesionstrength as being susceptible to delamination under external pressure,and they require heating at high temperatures so that they can not applyto a substrate not resistant to heat such as plastics, interiormaterials such as office walls and the surfaces of various productswhich are difficult to heat, and the like. In addition, there areproblems that the thermal treatments at high temperatures cause thephotocatalyst particles to reduce their specific surface area resultingin a reduction in their photocatalytic function. Moreover, there may berequired specific means such as devices for adhering under pressure, orfusing under heat.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a photocatalystcomposite comprising a substrate having photocatalyst particles adheredthereon via a less degradative adhesive.

Another object of the present invention is to provide a process forproducing the photocatalyst composite.

A further object of the present invention is to provide a coatingcomposition using the photocatalyst composite.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows variations in weight loss per unit area of theadhesives in the photocatalyst composites due to irradiation with theblack light for Samples A and C from Examples and Sample E fromComparative Example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present inventors have made a research to develop a process forachieving a firm adhesion of photocatalyst particles onto any substrateover an extended period of time without damaging the photocatalyticfunction of the particles. As a result, the present invention has beencompleted on the basis of the discovery that (1) when photocatalystparticles are adhered onto a substrate with an adhesive, thephotocatalytic function of the photocatalyst particles may decompose anddeteriorate the adhesive causing the photocatalyst particles to releasefrom the substrate, and however, the use of a less degradative adhesiveallows adhesion of the photocatalyst particles onto any substratewithout causing the release of the particles therefrom and unpredictablythe photocatalyst of the present invention to exhibit sufficientphotocatalytic function, (2) the photocatalyst particles may be adhere dto a substrate without lowering the photocatalytic function of theresultant photocatalyst composite when the amount of the photocatalystparticles is in the range of 5 to 98% based on the total volume of thephotocatalyst particles and the less degradative adhesive, (3) the useof organic adhesives such as fluorinated polymers and silicone basedpolymers or inorganic adhesives as less degradative adhesives results inmost reduced decomposition and degradation of the adhesives owing to thephotocatalytic function of the photocatalyst particles so that thephotocatalyst particles can be firmly adhered for a long time, andparticularly a fluorinated polymers comprising primarily a copolymer ofvinylethers and/or vinylesters and fluoroolefins are preferred, (4)preferred photocatalyst particles are titanium oxide which has a highphotocatalytic function, a high chemical stability and no toxicity, andthat (5) a process for adhering photocatalyst particles, which isapplicable to rendering relatively easily the surfaces of variousproducts photocatalytic and which enables the photocatalytic function tobe readily utilized in domestic appliances, comprises the steps ofdisposing photocatalyst particles and a less degradative adhesive on asubstrate and then fixing the adhesive as a preferably convenient andeasy process, or more particularly comprises the steps of disposingphotocatalyst particles and a less degradative adhesive by coating orspraying a coating composition containing the photocatalyst particles,the adhesive and a solvent on the surfaces of a substrate such asvarious products and then fixing the adhesive.

That is, the present invention lies in providing a photocatalystcomposite comprising any substrate having photocatalyst particles firmlyadhered thereon for an extended period of time without losing thephotocatalytic function of the particles.

The present invention is a photocatalyst composite comprising asubstrate having photocatalyst particles adhered via a less degradativeadhesive. As used in the present invention, the term “less degradativeadhesive” refers to an adhesive having an extremely reduced rate ofdecomposition due to the photocatalytic function possessed by thephotocatalyst particles in the range of 10% or less, preferably 5% orless, more preferably 3% or less, most preferably 1% or less expressedas a weight loss of the adhesive in the photocatalyst composite asmeasured by the method described in the Example below. A weight losshigher than 10% indicates undesirably vigorous decomposition ordegradation of the adhesive with a great amount of the photocatalystparticles being released. The less degradative adhesives to be used inthe present invention include, for example, inorganic adhesives such assilicon compounds such as water glass, colloidal silica,polyorganosiloxanes and the like, phosphates such as zinc phosphate,aluminum phosphate and the like, biphosphates, cement, lime, gypsum,enamel frits, glass lining glazes, plasters, organic adhesives such asfluorinated polymers, silicone based polymers and the like, and theseadhesives may be used in combination of two or more thereof.Particularly inorganic adhesives, fluorinated polymers and siliconebased polymers are preferred in view of adhesion strength. The cement tobe used include, for example, Portland cements such as rapid-hardeningcement, general-use cement, moderate heat cement, sulfate-resistingcement, white cement, oil well cement, and geothermal well cement,blended cement such as fly-ash cement, sulfated slag, silica cement, andblast furnace cement, aluminous cement and the like. The plaster to beused includes, for example, gypsum plaster, lime plaster, dolomiteplaster and the like. The fluorinated polymers to be used include, forexample, crystalline fluorinated resins such as polyvinyl fluorides,polyvinylidene fluorides, polyethylene trifluorochlorides, polyethylenetetrafluorides, tetrafluoroethylene-hexafluoropropylene copolymers,ethylene-polyethylene tetrafluoride copolymers, ethylene-ethylenetrifluorochloride copolymers, tetrafluoroethylene-perfluoroalkylvinylether copolymers, amorphous fluorinated resins such as perfluorocyclopolymers, vinylether-fluoroolefin copolymers, vinylester-fluoroolefincopolymers, various fluorinated elastomers and the like. Particularlyfluorinated polymers comprising primarily vinylether-fluoroolefincopolymers and vinylester-fluoroolefin copolymers are preferred becausethey are susceptible to less decomposition and degradation and easy tohandle. The silicone based polymers to be used include linear siliconeresins, acryl-modified silicone resins, various silicone elastomers andthe like.

As used in the present invention, the term “photocatalyst particles”refers to those capable of exhibiting photocatalytic function uponirradiation with a radiation having a wavelength corresponding to notless than the band gap energy. The photocatalyst particles to be usedinclude one or a combination of two or more of known metal compoundsemiconductors such as titanium oxide, zinc oxide, tungsten oxide, ironoxide, strontium titanate, and the like. Particularly titanium oxidewhich has a high photocatalytic function, a high chemical stability andno toxicity is preferred. In addition, it is preferred to include insidesaid photocatalyst particles and/or on the surfaces thereof at least onemetal and/or a compound thereof selected from the group consisting of V,Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Pt and Au as a second componentbecause of the higher photocatalytic function of the resultingphotocatalyst particles. The aforementioned metal compounds include, forexample, metal oxides, hydroxides, oxyhydroxides, sulfates, halides,nitrates, and even metal ions. The content of the second component mayvary depending upon the kind thereof. Preferred photocatalyst particleswhich may contain the aforementioned metals and/or metal compounds areof titanium oxide. The content of photocatalyst particles is preferablyin the range of 5 to 98% by volume based on the total amount of thephotocatalyst particles and the less degradative adhesive. The contentof the photocatalyst particles less than the above defined range tendsundesirably to result in a reduced photocatalytic function of theresulting photocatalyst, while that higher than the above defined rangetends also undesirably to cause a reduction in adhesion strength. Whencements or gypsum are used as less degradative adhesives, the content ofthe photocatalyst particles should be preferably from 5 to 40%, mostpreferably from 5 to 25%. Alternatively, when organic or inorganicadhesives other than the cement and gypsum are used as less degradativeadhesives, the content of the photocatalyst particles should bepreferably from 20 to 98%, more preferably 50 to 98% and most preferably70 to 98%.

The photocatalyst particles to be used in the present invention may beproduced by any one of known techniques. For example, there are severalmethods including (1) a method comprising thermally hydrolyzing atitanium compound such as titanyl sulfate, titanium chloride, titaniumalkoxides, and the like, if necessary, in the presence of seeds fornucleation, (2) a method comprising neutralizing a titanium compoundsuch as titanyl sulfate, titanium chloride, titanium alkoxides, and thelike, by adding an alkali, if necessary, in the presence of seeds fornucleation, (3) a method comprising oxidizing titanium chloride,titanium alkoxides, and the like in the vapor phase, and (4) a methodcomprising firing or hydrothermally treating the titanium oxidesproduced by any one of the methods (1) and (2). Specifically thosetitanium oxides obtained by the method (1) or by the hydrothermaltreatment at temperatures of 100° C. or higher are preferred because oftheir higher photocatalytic function. As used in the present invention,the term “titanium oxides” is meant to indicate those so-called hydratedtitanium oxide, hydrous titanium oxide, metatitanates, orthotitanates,titanium hydroxide, besides titanium oxide, regardless of their crystalsystem. In order to allow at least one metal and/or compound thereofselected from the group consisting of V, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd,Ag, Pt and Au as a second component to be present inside thephotocatalyst particles and/or on the surfaces thereof, one can employ amethod comprising adding the metal and/or the compound to be adsorbedduring the production of the photocatalyst particles, or a methodcomprising adding the metal and/or the compound to be adsorbed after theproduction of the photocatalyst particles, if necessary, under heat, orif necessary, using reduction.

The substrates to be used in the present invention include inorganicarticles such as ceramics and glasses, organic articles such asplastics, elastomers, woods and paper sheets, and metallic articles madeof a metal such as aluminum or an alloy such as steel. Dimensions andforms of the substrates are not critical. Even coated articles may beused.

In the present invention, it is preferred that both the photocatalystparticles and an adsorbent are adhered onto a substrate via the lessdegradative adhesive because there coexist an action adsorbing treatmentmaterials. The adsorbents to be used include general adsorbents such asactivated carbon, zeolites, silica gels, and the like.

In another aspect of the present invention, a first layer consisting ofan adhesive without containing any photocatalyst particles is providedon a substrate, and then a second layer consisting of a less degradativeadhesive and photocatalyst particles is provided on the first layer. Theprovision of the first layer containing no photocatalyst particleenables a firm connection between the substrate and the second layercontaining the photocatalyst particles resulting in a firmer adhesion ofthe photocatalyst particles onto the substrate sustainable for a longerperiod of time. Moreover, the first layer should preferably containinorganic particles having no photocatalytic function as filler. Suchinorganic particles to be used include those of titanium oxides, siliconoxide, aluminum oxide, magnesium oxide and the like, the surfaces ofwhich are coated with silicon oxide, aluminum oxide, or zirconium oxide.

The photocatalyst composite according to the present invention may beproduced by disposing photocatalyst particles and a less degradativeadhesive on at least a part of a substrate and then fixing the adhesiveto adhere the photocatalyst particles onto the substrate via theadhesive. In the present invention, specifically the photocatalystparticles and the less degradative adhesive should preferably bedispersed in a solvent to prepare a coating composition which is thencoated or sprayed on a substrate to dispose the photocatalyst particlesand the less degradative adhesive on at least a part of the substrate.The solvents to be used include water, and organic solvents such astoluene, alcohols, and the like. The less degradative adhesives to becontained in the coating composition include the aforementioned oneswhich should preferably be soluble to the solvents used. In the presentinvention, the less degradative adhesive contained in the coatingcomposition is preferably one or more polymers selected from the groupconsisting of a fluorinated polymer and a silicone based polymer. Theamount of the photocatalyst particles is in the range of 5 to 98% byvolume, preferably 20 to 98% by volume, more preferably 50 to 98% byvolume, and most preferably 70 to 98% by volume, based on the totalamount of the photocatalyst particles and the less degradative adhesive.The coating compositions may be formulated with cross linking agents,dispersants and fillers. The cross linking agents to be used includeordinary ones of isocyanate family and melamine family and thedispersants to be used include coupling agents. Particularly when thecontent of the photocatalyst particles in the coating composition is inthe range of 40 to 98% by volume based on the total amount of thephotocatalyst particles and the less degradative adhesive, it ispreferred to formulate the coating composition with a coupling agent.The amount of the coupling agents to be added should be preferably from5 to 50%, more preferably 7 to 30%.

The application of the coating composition may be accomplished bycoating or spraying according to any one of ordinary coating techniquesincluding immersing, dip-coating, spin-coating, blade coating, rollercoating, wire bar coating, reversal roll coating, or an ordinaryspraying technique such as spray coating to dispose the photocatalystparticles and the less degradative adhesive on at least a part of thesubstrate. If necessary, before the application of the photocatalystparticles and the less degradative adhesive onto the substrate bycoating or spraying, an organic adhesive such as acrylic resins, epoxyresins, polyester resins, melamine resins, urethane resins, alkyd resinsand the like, or such a less degradative adhesive as mentioned above maybe coated or sprayed onto the substrate to from a first layer and thenon the first layer there is provided a second layer consisting of thephotocatalyst particles and the less degradative adhesive by coating orspraying the coating composition. The organic adhesive may be of such akind as normally used.

After coating or spraying, the composition is fixed to produce thephotocatalyst composite of the present invention. The fixation may beperformed by a technique of drying, irradiating with ultraviolet rays,heating, cooling, or using a cross linking agent and it is achieved at atemperature lower than 400° C., preferably from room temperature to 200°C. In this regard, a temperature higher than 400° C. may undesirablycause thermal degradation of the adhesive rendering the photocatalystparticles readily releasable. The present invention prefers to employ amethod for fixation with cross linking agents of isocyanate family andmelamine family.

The photocatalyst composite according to the present invention can causepurification and sterilization of products containing deleteriousmaterials, malodorous materials and oily materials as well asdecomposition of such materials which come into the vicinity of thephotocatalyst particles by irradiating with a ray having a wavelengthcorresponding to not less than the band gap energy. The radiations to beused for the exposure include light rays including ultraviolet rays, forexample, the sun's rays, and lights from fluorescent lamp, black lamp,halogen lamp, xenon flash lamp, mercury lamp and the like. Particularlythe light rays including near ultraviolet rays of 300 to 400 nm arepreferred. The intensity and the time of irradiation with the light rayscan be determined routinely depending upon the amounts of materials tobe treated.

The present invention will be illustrated below with reference to someexamples.

EXAMPLE 1

To an acidic titania sol obtained by thermal hydrolysis of titanylsulfate (CS-N, available from Ishihara Sangyo Kaisha, Ltd.), there wasadded sodium hydroxide to adjust the pH to 7, followed by filtration andwashing. Then, to the resulting titanium oxide wet cake was added waterto prepare a slurry of 100 grams/liter expressed as TiO₂. Sodiumhydroxide was added to this slurry to adjust the pH to 10, and thenhydrothermal treatment was conducted in an autoclave at a temperature of150° C. for 3 hours. Then the slurry after the hydrothermal treatmentwas neutralized to pH 7 by adding nitric acid, filtered, and washed withwater, followed by drying at a temperature of 110° C. for 3 hours toyield titanium oxides.

Then, mixtures of compositions indicated below were shaked in a paintshaker for 3 hours to effect sufficient mixing, and dispersed to producea coating composition. The LUMIFRON LF 200C as referred to below is afluorinated polymer comprising primarily a copolymer of vinylether andfluoroolefin.

Titanium oxides 9.80 grams Florinated polymer (LUMIFRON LF200C, 0.80gram available from Asahi Glass Co., Ltd.) Isocyanate based curing agent0.16 gram Titanium coupling agent (PLANEACT 338X, 1.00 gram availablefrom Ajinomoto Co., Inc.) Toluene 23.60 ml

The coating composition of the above formulation was coated on a glassplate of 20 cm², and then dried at a temperature of 120° C. for 20minutes to produce a photocatalyst composite of the present invention(Sample A). This Sample A had a titanium oxide content of 90% by volumebased on the total amount of the titanium oxides and the lessdegradative adhesive.

EXAMPLE 2

By using the same titanium oxides as used in Example 1, the mixtures ofcompositions indicated below were shaked in a paint shaker for 3 hoursto effect sufficient mixing, and dispersed to produce a coatingcomposition.

Titanium oxides 7.64 grams Florinated polymer (LUMIFRON LF200C, 2.36gram available from Asahi Glass Co., Ltd.) Isocyanate based curing agent0.47 gram Titanium coupling agent 0.76 gram (PLANEACT 338X, availablefrom Ajinomoto Co., Inc.) Toluene 22.50 ml

The coating composition of the above formulation was coated on a glassplate of 20 cm², and then dried at a temperature of 120° C. for 20minutes to produce a photocatalyst composite of the present invention(Sample B). This Sample B had a titanium oxide content of 70% by volumebased on the total amount of the titanium oxides and the lessdegradative adhesive.

EXAMPLE 3

By using the same titanium oxides as used in Example 1, the mixtures ofcompositions indicated below were shaked in a paint shaker for one hourto effect sufficient mixing, and dispersed to produce a coatingcomposition.

Titanium oxides 9.8 grams Polyorganosiloxane based 2.7 grams inorganicadhesive (a mixture of T2202A and T2202B in a ratio of 3:1, availablefrom Japan Synthetic Rubber Co., Ltd.) Isopropyl alcohol 21.5 ml

The coating composition of the above formulation was coated on a glassplate of 20 cm², and then dried at a temperature of 180° C. for 10minutes to produce a photocatalyst composite of the present invention(Sample C). This Sample C had a titanium oxide content of 90% by volumebased on the total amount of the titanium oxides and the lessdegradative adhesive.

EXAMPLE 4

To an acidic titania sol obtained by thermal hydrolysis of titanylsulfate (CS-N, available from Ishihara Sangyo Kaisha, Ltd.), there wasadded sodium hydroxide to adjust the pH to 7, followed by filtration andwashing. Then, the resulting titanium oxide wet cake was dried at atemperature of 110° C. for 3 hours to obtained titanium oxides.

Then, the mixtures of compositions indicated below were shaked in apaint shaker for 3 hours to effect sufficient mixing, and dispersed toproduce a coat composition.

Titanium oxides 7.0 grams Polyorganosiloxane based inorganic 4.3 gramsadhesive (a mixture of T2202A and T2202B in a ratio of 3:1, availablefrom Japan Synthetic Rubber Co., Ltd.) Isopropyl alcohol 22.5 ml

The coating composition of the above formulation was coated on a glassplate of 20 cm², and then dried at a temperature of 180° C. for 10minutes to produce a photocatalyst composite of the present invention(Sample D). This Sample D had a titanium oxide content of 80% by volumebased on the total amount of the titanium oxides and the lessdegradative adhesive.

COMPARATIVE EXAMPLE 1

By using the same titanium oxides as used in Example 1, the mixtures ofcompositions indicated below were shaked in a paint shaker for one hourto effect sufficient mixing, and dispersed to produce a coatingcomposition.

Titanium oxides 9.8 grams Vinyl acetate-acryl copolymer 0.7 gram(BONCOAT 6290, available from Dainippon Ink & Chemicals, Inc.) Water24.8 ml

The coating composition of the above formulation was coated on a glassplate of 20 cm², and then dried at a temperature of 120° C. for 10minutes to produce a photocatalyst composite (Sample E). This Sample Ehad a titanium oxide content of 90% by volume based on the total amountof the titanium oxides and the adhesive.

The photocatalyst composites obtained in Examples and ComparativeExample (Samples A to E) were exposed to the black light at anultraviolet intensity of 7 mW/cm² on the surface of each Sample for 5hours. The adhesive in the photocatalyst composite was weighed beforeand after the irradiation with the black light to determine the weightloss. As a result, no weight loss was observed for the Samples A to D ofthe present invention indicating no decomposition of the adhesives.However, the Sample E of the Comparative Example without using any lessdegradative adhesive exhibited a weight loss of 85% indicating that mostof the adhesive was decomposed by the photocatalytic function oftitanium oxides. In addition, it was observed that the Sample E wasyellowed and the titanium oxide particles were partly released. Thevariation in the weight loss of the adhesive in the photocatalystcomposite owing to the irradiation with the black light for each of theSamples A and C from Examples and the Sample E from Comparative Exampleis shown in the FIGURE. The Samples A and B from Examples 1 and 2contained the coupling agents which were adsorbed on the surfaces of thephotocatalyst particles to bridge between the less degradative adhesiveand the photocatalyst particles so that the photocatalyst particles didnot come into direct contact with the adhesive rendering the latter lessdecomposable.

Next, each of the Samples A to D of the present invention was placed ina 3 liters glass vessel and acetaldehyde as a malodorous component wasadded to the vessel to a concentration of 90 ppm and then the vessel wassealed. Then, the vessel was exposed to a mercury lamp at an ultravioletintensity of 14 mW/cm² on the surfaces of each Sample for 60 minutes.After the irradiation, the concentration of acetaldehyde in the glassvessel was measured. The results are indicated in Table 1. The Samples Ato D achieved an efficient decomposition of acetaldehyde due to thephotocatalytic function of titanium oxides.

TABLE 1 Concentration of Sample acetaldehyde (ppm) Example 1 A 0.5Example 2 B 0.5 Example 3 C 30.0 Example 4 C 0.5

EXAMPLE 5

To an acidic titania sol obtained by thermal hydrolysis of titanylsulfate (CS-C, available from Ishihara Sangyo Kaisha, Ltd.), there wasadded sodium hydroxide to adjust the pH to 7, followed by filtration,washing, drying, and then pulverizing to produce titanium oxides. 0.2gram of the titanium oxides, 0.8 gram of white cement (available fromOnoda Cement Co., Ltd.) and 0.7 gram of water were mixed and the wholewas coated on a glass plate of an area of 50 cm2 and dried at roomtemperature to produce a photocatalyst composite of the presentinvention (Sample F). This Sample F had a titanium oxide content of 17%by volume based on the total amount of the titanium oxides and the lessdegradative adhesive.

EXAMPLE 6

The same procedure as in Example 5, except that 0.8 gram of DENCA highalumina cement (Hi, available from DENKI KAGAKU KOGYO K.K.) was employedinstead of the white cement, was repeated to produce a photocatalystcomposite of the present invention (Sample G). This Sample G had atitanium oxide content of 17% by volume based on the total amount of thetitanium oxides and the less degradative adhesive.

COMPARATIVE EXAMPLE 2

1.0 gram of the same white cement as used in Example 5 and 0.7 gram ofwater were mixed and the whole was coated on a glass plate having asurface area of 50 cm² and dried to produce Sample H.

COMPARATIVE EXAMPLE 3

1.0 gram of the same DENCA high alumina cement as used in Example 6 and0.7 gram of water were mixed and the whole was coated on a glass platehaving a surface area of 50 cm² and dried to produce Sample I.

Each of the Samples F to I from Examples and Comparatives Example wasplaced in a 4 liters vessel and standard nitrogen monoxide gas wasinjected into the vessel. Then, the vessel was exposed to the rays fromthe black light at an ultraviolet intensity of 1 mW/cm² on the surfacesof each Sample and the concentration of NOx gases in the glass vesselwas measured with time by means of a NOx sensor (11L, available fromGASTEC Co. Ltd.). The results are indicated in Table 2. The Samples Fand G from Examples 5 and 6 caused a great reduction in NOx gasconcentration, while the Samples H and I from Comparative Examples 2 and3 caused little variation in NOx gas concentration. It has been foundfrom this fact that the photocatalyst of the present invention iseffective for removing nitrogen monoxide by oxidation thereof. In theprocedure as described above, the weight of the cement in each of theSamples F and G was measured to evaluate the weight loss of the cement.No weight loss was observed indicating no decomposition of the cement.

TABLE 2 Concentration of NOx (ppm) after Sample 0 min. 10 min. 20 min.30 min. Example 5 F 18.8 8.9 3.1 1.2 Example 6 G 13.5 0.3 0 0 Comp. H15.5 13.5 13.5 13.5 Example 2 Comp. I 13.5 13.2 10.6 10.6 Example 3

EXAMPLE 7

All the coating composition obtained by repeating the procedureidentical to that in Example 1 was coated on a transparent acrylic platehaving a surface area of 100 cm² and dried at a temperature of 120° C.for 20 minutes to produce a photocatalyst composite of the presentinvention (Sample J). This Sample J had a titanium oxide content of 90%by volume based on the total amount of the titanium oxides and the lessdegradative adhesive.

COMPARATIVE EXAMPLE 4

The same acrylic plate as used in Example 7 was employed as Sample K.

Each of the Samples J and K from the aforementioned Example andComparative Example was on the inner walls of a 50 liters water bath. 45liters of water and 20 goldfish (Wakin) were placed in the bath andirradiated externally with the light rays from two 20 W fluorescentlamps.

After the goldfish was raised for two weeks, it was observed that algaewere deposited on the surfaces of the Sample K from Comparative Example4, while no deposition of algae wds observed on the surfaces of theSample J from Example 7. This is because even when algae were depositedon the surfaces of the Sample J from Example 7, they were immediatelydecomposed by the photocatalytic function. In the procedure as describedabove, the fluorinated polymer in the Sample J was measured for theweight loss. No weight loss was observed indicating no decomposition ofthe fluorinated polymer.

EXAMPLE 8

The same procedure as in Example 7 was repeated, except that a mixtureof the composition indicated below was shaked in a paint shaker for onehour to effect sufficient mixing and dispersed to produce a coatingcomposition which was all coated on a transparent acrylic plate by meansof a spin coater (1000 r.p.m.×10 sec) and that the resulting transparentacrylic plate having a first layer consisting of the less degradativeadhesive without any photocatalyst particles on the surface thereof wasused as a substrate, to produce a photocatalyst of the present invention(Sample L). The content of titanium oxides, i.e. the photocatalystparticles in the second layer, of this Sample L was 90% by volume basedon the total amount of the titanium oxides and the less degradativeadhesive.

Titanium oxides having no photocatalytic 3.3 grams function (CR-90,available from Ishihara Sangyo Kaisha, Ltd.) Florinated polymer(LUMIFRON LF200C, 5.5 grams available from Asahi Glass Co., Ltd.)Isocyanate based curing agent 1.1 grams Toluene 20.7 ml

Measurements of the weight loss of the adhesive used for Sample L in theaforementioned procedures revealed that there was found no weight changein Sample L of the present invention, and the adhesive was notdegradated and the titanium oxide photocatalyst particles were notreleased from the substrate. The film strength of Sample L of Example 8was 3H in terms of pencil hardness, which means that the photocatalystparticles were firmly adhered. Furthermore, the Sample L was placed in aflow of water and irradiated with the black light in such a manner thatthe superficial ultraviolet intensity was 2 mW/cm² for 3 weeks. However,there was observed no releasing of the titanium oxide photocatalystparticles from the substrate.

EXAMPLE 9

The same procedure as in Example 1 was repeated, except that titaniumoxide particles coated with a zinc compound were used instead of thetitanium oxides, to produce a photocatalyst composite of the presentinvention (Sample M). The content of the photocatalyst titanium oxideparticles coated with the zinc compound in this Sample M was 90% byvolume based on the total amount of the photocatalyst particles and theless degradative adhesive.

The titanium oxide particles coated with the zinc compound were preparedas follows:

Water and sodium hydroxide were added to a slurry of titanium oxideobtained by thermally hydrolyzing titanyl sulfate to form a slurryhaving a pH of 10 and 100 grams/liter expressed as TiO₂. This slurry wassubjected to the hydrothermal treatment in an autoclave at 150° C. for 5hours and then neutralized with nitric acid, filtered and washed withwater. To the resultant titanium oxide wet cake was added water toprepare a slurry containing 100 grams/liter expressed as TiO₂. To theresultant slurry was added hydrochloric acid to form the slurry having apH of 4. To one liter of this slurry was dropwise added 7.2 ml of anaqueous 1 mol/liter zinc chloride solution under stirring. Then, theslurry was neutralized with a 2N sodium hydroxide solution, filtered andwashed with water. Thereafter, the resultant product was dried at 120°C. for 16 hours and pulverized to form titanium oxide particles having azinc compound carried thereon in a ZnO:TiO₂ ratio of 1:99.

EXAMPLE 10

The same procedure as in Example 1 was repeated, except that titaniumoxide particles coated with an iron compound were used instead of thetitanium oxides, to produce a photocatalyst composite of the presentinvention (Sample N). The content of the photocatalyst titanium oxideparticles coated with the zinc compound in this Sample N was 90% byvolume based on the total amount of the photocatalyst particles and theless degradative adhesive.

The titanium oxide particles coated with the iron compound were preparedas follows:

10 grams of titanium oxides obtained by hydrolysis under heat of titanylsulfate were used to prepare a slurry of 100 grams/liter expressed asTiO₂. 2.9 ml of an aqueous solution of ferric chloride (FeCl₃.6H2O) atconcentration of 5 grams/liter were added to the slurry and stirring wascontinued for one hour. Thereafter a diluted aqueous ammonia was addedto the slurry to adjust the pH to 7. After the slurry was stirred forone hour, the slurry was filtered, washed with water, and dried at atemperature of 110° C. for 3 hours to yield titanium oxide particlescoated with the iron compound.

These titanium oxide particles had iron compounds thereon in an Fe/TiO₂ratio of 300 ppm.

EXAMPLE 11

The same procedure as in Example 10 was repeated, except that theconcentration of the aqueous solution of ferric chloride was 50grams/liter, to produce a photocatalyst of the present invention (SampleO). The content of the photocatalyst titanium oxide particles coatedwith the iron compound in this Sample O was 90% by volume based on thetotal amount of the photocatalyst particles and the less degradativeadhesive.

These titanium oxide particles had iron compounds thereon in an Fe/TiO₂ratio of 3000 ppm.

EXAMPLE 12

The same procedure as in Example 1 was repeated, except that 8.9 gramsof TiO₂ and 0.5 gram of active carbon were used, to prepare aphotocatalyst composite according to the present invention (Sample P).The total amount of the titanium oxide and the active carbon of Sample Pwas 90% by volume based on the total amount of the titanium oxide,active carbon and less degradative adhesive.

EXAMPLE 13

The same procedure as in Example 12 was repeated, except that the activecarbon was placed with a zeolite in an amount of 0.8 gram, to prepare aphotocatalyst composite according to the present invention (Sample Q).The total amount of the titamium oxide and the zeolite was 90% by volumebased on the total amount of the titanium oxide, zeolite and lessdegradative adhesive.

Observation of the less degradative adhesive in each of Samples L to Qrevealed that there was found no weight loss. In other words, the lessdegradative adhesive of Samples L to Q was not degraded, and thetitanium oxide particles were not released from the substrate.

Next, each of the Samples A, N and O of the present invention was placedin a 0.8 liter glass vessel and acetaldehyde as a malodorous componentwas added to the vessel to a concentration of 100 ppm and then thecontainer was sealed. Then, the vessel was left to stand for 30 minutesand then irradiated with the black light at an ultraviolet intensity of1 mW/cm² on the surfaces of each Sample for 60 minutes. After theirradiation, the concentration of acetaldehyde in the glass vessel wasmeasured. The results are shown in Table 3. The Samples A, N and Odecomposed effectively the acetaldehyde due to the photocatalyticfunction of titanium oxides.

TABLE 3 Concentration of Sample acetaldehyde (ppm) Example 1 A 10.5Example 10 N 2.0 Example 11 O 0.4

Then, Samples M, P and Q were separately placed in respective 0.8-literglass vessels. Malodorous methylmercaptan was added to the glass vesselsin a concentration of about 500 ppm. Then, the vessels were sealed.Then, these vessels were left to stand for 2 hours without anyirradiation with ultraviolet rays, and irradiated for 60 minutes withthe black light in such a manner that the ultraviolet intensity on eachof the samples was 1 mW/cm². After the irradiation, the concentration ofthe methylmercaptan in the vessels was measured. The results are shownin Table 4. From Table 4, it is clear that the methylmercaptan waseffectively removed due to the function of the photocatalyst particlesof Samples M, P and Q.

TABLE 4 Concentration of Sample Methylmercaptan (ppm) Example 9 M 72Example 12 P 90 Example 13 Q 125 

In the aforementioned examination, the concentration of themethylmercaptan in the vessels left to stand for 2 hours withoutirradiation with ultraviolet rays was 250 ppm for each of the samples.The concentration of metylmercaptan in the vessels left to stand forfurther one hour without irradiation with ultraviolet rays was 240 ppmfor Samples M and Q and 220 ppm for Sample P.

The photocatalyst composite of the present invention comprises asubstrate having photocatalyst particles thereon via a less degradativeadhesive, and causes very little decomposition and degradation of theadhesive owing to the photocatalytic function. The present inventionenables long-term firm adhesion of photocatalyst particles onto anysubstrate without damaging the photocatalytic function. The utilizationof the photocatalyst composite of the present invention allows effectiveand prompt removal of deleterious materials, malodorous materials, oilycomponents, bacteria, actinomyces, fungi, algae and the like. Therefore,the photocatalyst composite is very useful as deodorant and sterilizerboth at home and in industry. In addition, the photocatalyst compositeof the present invention can be used for an extended period of time, hasa high degree of safety, finds applicability to a wide variety ofdeleterious materials, and is disposable without polluting theenvironment. Thus, it is very useful in industry. In the process forproducing the photocatalyst composite according to the presentinvention, the use of fluorinated polymers as less degradative adhesivesenables production of preferred photocatalyst composites, the surfacesof which have a lesser tendency to adsorb dust and contaminants due toweak sticking power of the fluorinated polymers.

The process for producing the photocatalyst composite according to thepresent invention is a useful process which can employ any materialssuch as plastics as substrate and produce conveniently and easilyconsistent quality photocatalyst composites.

The coating composition of the present invention can be coated orsprayed onto substrates of any form or desired sites thereof, and allowsthe ready utilizing of the photocatalytic function. Thus, particularlyit is useful for domestic applications.

What is claimed is:
 1. A method for removing NOx comprising the steps ofexposing a photocatalyst composite for removing NOx to an atmospherecontaining NOx wherein the photocatalyst composite includes a mixture ofphotocatalyst particles having a photocatalytic function with cement asa less degradative adhesive adhered on a substrate.
 2. The method forremoving NOx according to claim 1, wherein the amount of saidphotocatalyst particles having a photocatalytic function is within therange of 5 to 40% by volume based on the total amount of saidphotocatalyst particles and said less degradative adhesive.
 3. Themethod for removing NOx according to claim 1, wherein on the substrateis provided a first layer comprising an adhesive without containing anyphotocatalyst particles and further on said first layer is provided asecond layer comprising said mixture of said photocatalyst particleswith said less degradative adhesive.
 4. The method for removing NOxaccording to claim 1, wherein said photocatalyst particles comprise atleast one selected from the group consisting of metals and metalcompounds of V, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Pt and Au as asecond component inside each of said photocatalyst particles and/or onthe surfaces thereof.
 5. The method for removing NOx according to claim1, wherein said photocatalyst particles are of titanium oxide.